There are many industrial applications for techniques that enable controlled patterning of surfaces, such as in the fabrication of semiconductor wafers and data storage media. Advances in patterning technology (including techniques like electron-beam lithography, two-photon processing, electrohydrodynamic lithography and nano-imprint lithography) have also enabled new functional materials and smaller, more complex features, opening up new markets in areas ranging from solar cells and displays to antibacterial coatings for consumer products.
Optical lithography in particular has been established as a cost-effective method for patterns with feature dimensions of more than 100 nm. However, methods for controlled patterning in the nanoscale range (and in particular less than 100 nm) are still expensive and inefficient. In particular, methods like electron beam lithography require expensive equipment investments and have low throughput, especially for writing dense patterns over large-area substrates.
Since its introduction, nanoimprint Lithography (“NIL”) has emerged as a simple alternative with low cost and high throughput that lends itself to three-dimensional patterning through various modifications of the process. Furthermore, rapid development of this technique in the past decade has expanded its potential to fabricate features smaller than 100 nm. However, NIL is not without its drawbacks, which for example include expensive consumables, high error-rates and an inherent limitation to about 1:1 pattern replication.
NIL defines patterning through deformation of materials under suitable pressure and temperature. In a known process for NIL, a thin layer of imprint resist (thermoplastic polymer) is spin-coated onto a sample substrate. A mold having predefined topological patterns is brought into contact with the sample and pressed into the polymer coating under a certain pressure and at a temperature above the glass transition temperature of the polymer to allow the pattern on the mold to be pressed into the melt polymer film. After being cooled down, the mold is separated from the sample and the pattern resist is left on the substrate. A pattern transfer process, such as reactive ion etching (RIE) is used to transfer the pattern in the resist to the underneath substrate by removal of residue from the substrate.
Conventional photolithography can be relied upon for low-cost fabrication of imprint molds for patterns with dimensions larger than the nanoscale range, and in particular above 100 nm. However, molds with nanoscale features require the use of methods such as electron-beam lithography, which are often relatively expensive.
Currently, NIL is carried out by first imprinting a polymeric etch mask and etching a pattern onto the substrate, before subsequently patterning the substrate with metals, metal oxides, semiconductors or semiconductor oxides. This may result in an increased level of defects resulting from the use of an elaborative lithographic process.
There is a need to provide a method of preparing a substrate with dimensions in the nanoscale range, particularly 100 nm or less, that overcomes or at least ameliorates one or more of the disadvantages described above.
There is a need to provide a method to directly pattern metal and metal oxide structures, as well as semiconductor and semiconductor oxide structures, onto a substrate.